1. Field of the Invention
The present invention relates to a microfilm projecting appartus which guides the microfilm image-projecting light to the screen and photoreception means. The microfilm projecting apparatus in the present invention includes a microfilm scanner having a CCD line sensor as the photoreception means for converting an image of a microfilm into electric data, a microfilm reader printer having a photoconductive member as the photoreception means for printing an image of a microfilm on a paper, and so on.
2 . Description of Related Art
Any conventional microfilm projecting apparatus measures light of the microfilm image for detecting the density and the position of the image. It is essential for the microfilm projecting apparatus to execute measurement of light before photoreception means processes the microfilm image.
FIG. 1 is a schematic diagram representing an example of the optical system of a conventional microfilm scanner. This optical system is provided with optical-path switching mirror M1 which switches the image projection path into screen S or the line sensor L composed of a CCD. In FIG. 1, M2 and M3 are respectively the scan mirrors, whereas M4 is the stationary reader mirror. This optical system measures light of the microfilm image before the start of the scanning mode in which the microfilm image is scanned. After allowing the optical-path switching mirror M1 to swing itself back to the shelter positon shown by broken line, the optical system executes a light-measuring operation. Concretely, only after the optical-path switching mirror M1 has completed the sheltering movement, scan mirrors M2 and M3 are allowed to move themselves in order that the projected light can be led to the line sensor L before the optical system actually starts the microfilm image light measuring process.
Another example of the optical system of a conventional microfilm scanner shown in FIG. 2 switches the image projection path A without the provision of the optical path switching mirror M1 used for the example shown in FIG. 1. Concretely, while the reader mode is underway, this optical system forming the image projection light path A is oriented to the screen S via the stationary mirrors M5 and M6. This system executes the measurement of light by preliminarily moving the scan mirror M2 into the image projection light path A to thereby guide the projected light to the line sensor L via the scan mirrors M2 and M3.
Nevertheless, any of these conventional microfilm projecting apparatuses still has technical problems to solve as pointed out below.
Referring now to the time chart shown in FIG. 3 showing the operation timing of the prior art shown in FIG. 1, problems are explained below. While the optical-path switching mirror M1 moves itself, i.e., while the optical-path-switching operation is underway, the conventional microfilm projecting apparatus shown in FIG. 1 does not execute the light measurement. Only after completing the optical-path switching operation, this apparatus executes the light measurement. On the other hand, the conventional microfilm projecting apparatus shown in FIG. 2 needs to preliminarily move the scan mirror M2 for switching the optical path before the measurement of light.